Electric motors are comprised of a stationary portion or stator and a rotating portion called an armature or a rotor. In a DC motor, the stator produces a static electric field using either an electromagnet or a permanent magnet. The armature (rotor) consists of an electromagnet on a shaft that is connected to a commutator on the same shaft. The armature spins due to the coupling of the magnetic field produced by the current flowing through the armature electromagnet and the perpendicular magnetic field of the stator magnet. To maintain constant motion through a full rotation of the armature, the current in the armature electromagnet must reverse direction as it approaches poles of opposite polarity. In a brushed DC motor, this switching is accomplished mechanically through the interaction of brushes and a commutator. The armature electromagnet can have any number of poles depending on the size of the motor and the specific application it is being used in.
In an AC slip ring motor, the magnetic field inside the rotor generates a current in the windings of the stator. Brushes contact a slip ring to pass current to the slip ring, which in turn passes the current to the rotor. The current flowing through the slip ring to the rotor creates magnetic poles that alternate with respect to the stator as the rotor rotates. The alternating magnetic fields, in turn, induce an alternating current in the stator.
Other applications, such as linear motors, linear current transfer systems, and systems to energize rotating field coils, utilize a brush-type contact to pass current to a sliding member. As used herein, sliding includes moving in a linear or a rotational direction.
An electric motor or other device using brushes generally has a system called a brush holder or brushcard mounted to the stator to hold the brushes in a fixed orientation to the rotating portion of the armature (in the case of a motor) with sufficient pressure to maintain good contact with one brush face on the commutator or slip ring. The face of the brush that is in contact with the commutator or slip ring is known as the contact face. Springs are used to bias the brushes in order to ensure the contact face maintains contact with the commutator or slip ring. Such springs can be located to the rear or side of the brush. For example, a compression coil spring in the brushholder applies force to the face opposite of the contact face, which pushes the brush forward to maintain contact with the commutator or slip ring. The face opposite of the contact face is referred to as the non-contact face.
During the manufacture of the motor or other device using brushes, the commutator or slip ring must be inserted into the brush holder to make contact with the brushes. Because the brushes are biased toward the commutator or slip ring, something must retain the brushes in the brush holder to allow for the insertion of the commutator or slip ring into the brush box assembly. A separate disposable or reusable brush retention device is used by the prior art to retain the brushes. For example, in one prior art method, a tube is placed in between the brushes to retain them, then is displaced as the commutator or slip ring is installed. This use of such a tube prevents the insertion of the commutator or slip ring into a “blind” hole, e.g. into a closed end brush holder, because the displaced tube must be removed. Alternatively, pins or clips are used to retain the brushes until the commutator or slip ring assembly is installed. After installation, the pins or clips must be removed. These methods of manufacture add extra steps and add extra devices to the manufacture of electric motors and other device using brushes.